Passive devices for coupling optical signals are well-known to those of skill in the art. U.S. Pat. No. 4,590,619 to Weiner discloses a star coupler for an optical data bus system including a plurality of incoming and outgoing optical waveguides. In one embodiment, the coupler includes a mixing plate fitted with parallel oriented input and output fibers.
U.S. Pat. No. 4,995,692 discloses and claims an optical star coupler based on a curved optical ribbon as the mixing element. Optical fibers are optically connected to the ribbon element by way of a multi-apertured block.
U.S. Pat. No. 4,484,794 to Witte et al. shows a multi-layer star coupler wherein optical fibers are optically coupled by preparing three multi-layer structures followed by cementing them together. Similarly, a multi-piece mixing element may be found disclosed in U.S. Pat. No. 4,653,845 to Tremblay et al.
Optical mixing elements having a rectangular body with a thickness approximately equal to that of an optical fiber have been suggested in U.S. Pat. No. 4,449,783 to Witte. Such elements are reported to have relatively low insertion loss, but may in fact be as tedious to fabricate as the bundle-type star coupler taught by Coutandin et al., See U.S. Pat. No. 4,919,851.
In International Publication No. WO 90/08030 there is disclosed a star coupler partially made by way of an injection molding process. In accordance with the '030 publication, a coupler is molded in the negative in the sense that channels are defined by way of a molded body, which channels are then filled with a suitable optically clear material. In use, the material filling the channel is operative as a waveguide core material and the injection molded body is intended to function as cladding.
Despite substantial improvements in the field, known optical signal couplers tend to have unacceptably high losses, nonuniform signal distribution, or are inordinately difficult to fabricate.